This invention generally relates to metallurgical casting processes, and more specifically to a method and apparatus for removal of a sand core from a casting and the heat treatment of the casting.
A traditional casting process for forming metal castings employs one of various types of molds for example, a green sand mold, a precision sand mold, or a steel die, having the exterior features of a desired casting, such as a cylinder head or engine block, formed on its interior surfaces. A sand core comprised of sand and a suitable binder material and defining the interior features of the casting is placed within the mold or die. Sand cores generally are used to produce contours and interior features within the metal castings, and the removal and reclaiming of the sand materials of the cores from the castings after the casting process is completed is a necessity. Depending upon the application, the binder for the sand core and/or sand mold, if used, may comprise a phenolic resin binder, a phenolic urethane xe2x80x9ccold boxxe2x80x9d binder, or other suitable organic binder material. The mold or die is then filled with a molten metallic alloy. When the alloy has solidified, the casting generally is removed from the mold or die and may be then moved to a treatment furnace(s) for heat-treating, reclamation of the sand from the sand cores, and, at times, aging. Heat treating and aging are processes that condition metallic alloys so that they will be provided with different physical properties suited for different applications.
In accordance with some of the prior art, once the casting is formed, several distinctly different steps generally must be carried out in order to heat treat the metal casting and reclaim sufficiently pure sand from the sand core. A first step separates portions of sand core from the casting. The sand core is typically separated from the casting by one or a combination of means. For example, sand may be chiseled away from the casting or the casting may be physically shaken or vibrated to break-up the sand core and remove the sand. Once the sand is removed from the casting, heat treating and aging of the casting generally are carried out in subsequent steps. The casting is typically heat treated if it is desirable to, among other treatments, strengthen or harden the casting or to relieve internal stresses in the casting. An additional step consists of purifying the sand that was separated from the casting. The purification process is typically carried out by one or a combination of means. These may include burning the binder that coats the sand, abrading the sand, and passing portions of the sand through screens. Therefore, portions of sand may be re-subjected to reclaiming processes until sufficiently pure sand is reclaimed.
There is, therefore, a desire in the industry to enhance the process of heat treating castings and reclaiming sand core materials therefrom such that a continuing need exists for a more efficient method, and associated apparatus, that allow for more efficient heat treatment, sand core removal, and reclamation of sufficiently pure sand from the sand core.
Briefly described, the present invention comprises a system and method for heat treating castings, such as for use in a metallurgical plant, and for removing the sand cores used during the casting processes. The present invention encompasses multiple embodiments for efficiently removing and reclaiming the sand of sand cores using high pressure fluid media, and for in-mold heat treatment of the castings.
In one embodiment of the present invention for sand core removal and heat treatment of castings, a molten metal is poured into molds or dies that are typically preheated to maintain the temperature of the metal close to a heat treatment temperature as the castings are formed in the molds. The castings are then removed from their molds and are each placed in a pre-defined position on a saddle that has known x, y and z axes and coordinates. Each saddle generally is configured to receive a casting in a fixed orientation or position with the x, y, and z coordinates of the casting located in a known, indexed position or orientation so that the core apertures of the castings formed by the sand cores are oriented or aligned in known, indexed positions. The saddles further can include locating devices to guide and help maintain the castings in their desired, known indexed position.
Each saddle, with a casting positioned therein, is moved through a heat treatment furnace or chamber of a heat treatment station for heat treatment and core removal, and also potentially the reclamation of the sand cores. While passing through the heat treatment station for heat treatment, a series of nozzles with x, y and z coordinates that are fixed or set in alignment with the position of castings direct flows of high pressure, heated fluid media, such as heated air, or other fluid media, onto and into the castings. The fluid flows tend to dislodge and aid in removal of the sand of the sand cores from the internal cavities of the castings as the sand cores are broken down in the heat treatment station. Typically, the nozzles are arranged in a series of nozzle stations positioned sequentially through the heat treatment chamber, with the nozzles of each nozzle station oriented in a pre-defined arrangement corresponding to the known positions of the core apertures of the castings, and each nozzle assembly can be controlled remotely through a control system or station.
In another embodiment of the invention, the castings can be left in their molds or dies for xe2x80x9cin-diexe2x80x9d or xe2x80x9cin-moldxe2x80x9d heat treatment of the castings. The molds or dies typically are pre-heated before the molten metal of the castings is poured into them to maintain the metal close to a heat treatment temperature for the castings, so as to at least partially heat treat the castings inside the dies while and after the castings solidify. Thereafter, the molds or dies, with their castings therein, typically are located or placed in indexed orientations or positions with their x, y and z coordinates known for heat treatment of the castings therein and removal of the sand cores.
For heat treatment and the removal and reclamation of the sand cores of the castings, the castings and sometimes the molds or dies generally are passed through a heat treatment furnace of a heat treatment station. The heat treatment station further includes a plurality of nozzle stations each having a series of nozzles oriented or positioned in a pre-defined manner corresponding to the known positions of the molds or dies and castings for applying high pressure fluids thereto. The nozzle stations also can include robotically operated nozzles that move along a pre-defined path around the molds or dies, into various application positions corresponding to the positions or orientations of access openings or apertures in the molds or dies for access to the castings for dislodging the sand cores from the castings. Alternately, the heat treatment station can also include alternative energy sources, such as inductive or radiant energy sources, or a heated oxygen chamber or a heated fluidized bed, for supplying energy to the dies or mold packs to raise their temperature for heat treating the castings therewithin. Thereafter, the castings are removed from their molds or dies and are passed through subsequent core removal stations or processes to further remove and potentially reclaim the sand cores from the castings.
In a further embodiment, the molds or dies are pre-heated to a pre-defined temperature. Thereafter, as molten metal is poured into the dies, the dies continue to be heated to heat treat castings as they are solidified without removing the castings from the dies. The dies can then be transferred to a quenching station for quenching of the castings and removal of the sand cores therefrom. In this embodiment, the dies generally are maintained in a known, fixed position or orientation at or adjacent to the pouring station. The dies are heated by the application of heated fluids from a series of nozzles positioned about the dies, typically in alignment with die access openings thereof. The nozzles further are subsequently moved about the dies between a series of nozzle positions set according to the position or orientation of the dies, for heating the dies to heat treat the castings within the dies. Alternately, the mold or die may be placed, at least partially, in a temperature-controlled fluid bed for heating or otherwise controlling the mold or die temperature for heat treating the castings and possibly accomplishing other purposes.
Various objects, features, and advantages of the present invention will become apparent upon reading and understanding this specification, taken in conjunction with the accompanying drawings.